FIELD OF THE INVENTION
The invention relates to a method for entering and leaving a power-saving operation of a subscriber in an annular communication network, in which data are transmitted in a format that prescribes a pulsed sequence of individual bit groups of identical length in which specific bit positions are reserved for a preamble that is decoded in a receive circuit of each subscriber. The invention also relates to such a method in a mobile annular communication system, in particular in a motor vehicle.
The subscribers of the communication network are data sources and data sinks which are interconnected through data lines that form a ring feeder. Both source data and control data can be transmitted between the subscribers through the ring feeder by subdividing the bit groups into component bit groups which respectively form a data channel. A clock signal is generated by a single subscriber and transmitted through the net in the form of specific preamble codes which respectively identify the start of a block, which is formed in each case by a combination of a plurality of bit groups. All of the other subscribers detect the block start code and are synchronized with the clock signal with the aid of successive block start codes. It is noted that purely packet-oriented data transmission methods such as, for example, ATM methods, that is to say asynchronous transmission methods, are to be distinguished therefrom.
Such an annular communication network as is described, for example, in Published European Patent Application 0 725 522 A1 serves for networking different types of electric and electronic devices which are intended to exchange information among one another in a partly complicated way, with the aid of data lines of physically simple construction. The subscribers can exchange both source data and control data through those data lines. For example, in the audio field it is possible to transmit audio data from data sources such as CD players, radio receivers and cassette recorders to data sinks such as amplifier/loudspeaker combinations, and control data can be transmitted at the same time, for example to control volume. In that case, a device can be constructed simultaneously as a data source and a data sink, such as is the case with a cassette recorder, for example.
In order to realize power-saving functions in such a communication network, individual subscribers have previously been turned off completely upon external command or after the expiration of a preset time of inactivity. In order to reactivate such a turned-off subscriber, it has been necessary for the entire network to be turned off and turned on again.
It is desirable to be able to reactivate a deactivated subscriber when required, in particular through the use of a subscriber which manages the network, without having to turn off the entire network and turn it on again or without carrying out a reset.
There are special wakeup circuits for such a purpose which monitor the signal on a data line and which react to a specific modulated signal by again turning on the subscriber connected to the wakeup circuit. However, such a circuit, which each subscriber with a power-saving function must have, is relatively expensive and takes up a lot of space in relative terms.